Patent Application
20140190003
The present invention relates to inductors, and more particularly, this invention relates to thin film ferromagnetic inductors having at least one laminated yoke,
The integration of inductive power converters onto silicon is one path to reducing the cost, weight, and size of electronics devices. One main challenge to developing a filly integrated power converter is the development of high quality thin film inductors. Thin film inductors for power conversion applications should store a large amount of energy per tit area to fit in the limited space on silicon. To accomplish this, ferromagnetic materials are used to increase the energy stored for a given current. However, ferromagnetic materials also introduce some disadvantages. Magnetic materials operating at high frequency produce losses through eddy currents and hysteresis. The eddy currents are created when the time varying magnetic fields in the yokes create an electric field that drives a circular current flow. These losses can be substantial and increase with the thickness of the yoke, and driving frequency of the inductor. Hysteresis losses can be created by magnetic domain walls in the yoke material. To enable efficient power conversion it is therefore critical to reduce the eddy current and hysteresis losses in the yokes.
A method according to one embodiment includes forming a bottom yoke above a substrate; forming one or more conductors above the bottom yoke and separated therefrom by an insulating material; and forming a top yoke above the one or more conductors and separated therefrom by an insulating material. At least one of forming the bottom yoke and forming the top yoke includes a procedure comprising: applying a first mask; depositing a first ferromagnetic layer in an area not masked by the first mask; depositing a nonmagnetic layer above the first ferromagnetic layer; applying a second mask above the nonmagnetic layer; and depositing a second ferromagnetic layer in an area not masked by the second mask.
Other aspects and embodiments of the present invention will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the invention.
The following description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations.
Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc.
It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless otherwise specified.
The following description discloses several preferred embodiments of thin film inductor structures having conductors surrounded by a ferromagnetic yoke with a magnetic top section and a magnetic bottom section. At least one of the yokes is laminated. The resulting inductors, according to various embodiments, exhibit a reduced loss due to eddy currents.
Thin film inductor technology is one path to integrating power conversion onto silicon, which can bring about a number of advantages including reduced cost, weight, and size of electronics devices. The thin film inductor technology may also become important for future microprocessor power conversion needs where the proximity of the power converter to the processor brings about many advantages.
Thin film inductors for power conversion applications should store a large amount of energy per unit area to fit in the limited space on silicon. To accomplish this, ferromagnetic materials are used to increase the energy stored for a given current. However, ferromagnetic materials also introduce some disadvantages. Magnetic materials operating at high frequency produce losses through eddy currents and hysteresis.
The eddy currents are created when the time varying magnetic fields in the yokes create an electric field that drives a circular current flow. These losses can be substantial d increase with the thickness of the yoke, and driving frequency of the inductor. Hysteresis losses can be created by magnetic domain walls in the yoke material. To enable efficient power conversion it is therefore critical to reduce the eddy current and hysteresis losses in the yokes.
One method of reducing the losses while retaining a large yoke thickness is to construct the yoke out of multiple layers of magnetic material separated by insulating or non-magnetic spacer layers. In the case of insulating spacer layers, each spacer prevents current from flowing between the adjacent magnetic layers and thus reduces the eddy current losses. The advantage in this case depends on the resistivity of the layers. In the case of conductive non-magnetic layers there is no reduction of eddy current, however the separation of the magnetic layers allows the magnetization in adjacent yoke layers to be oriented in opposite directions with flux closure at the edges of the structure. This can eliminate domain walls from the inductor and significantly reduce hysteresis losses.
In various embodiments of the present invention, one or more insulators are incorporated, thereby effectively separating the area of the yoke into thinner laminated layers. The laminations may be placed in the yokes in order to reduce the losses in the yokes. In other approaches, a nonmagnetic layer may be used to separate laminated layers of the yoke. The nonmagnetic layer may or may not be electrically insulating.
In one general embodiment, a thin film inductor includes a bottom yoke; a top yoke above the bottom yoke; one or more conductors passing between the yokes and separated therefrom by an insulating material; wherein at least one of the yokes has a laminate structure comprising a first ferromagnetic layer, a nonmagnetic layer above the first ferromagnetic layer, and a second ferromagnetic layer above the first ferromagnetic layer, wherein a width of the first ferromagnetic layer is different than a width of the second ferromagnetic layer in a direction parallel to a plane of deposition of the first ferromagnetic layer.
In another general embodiment, a system includes an electronic device; and a power supply or power converter incorporating a thin film inductor as recited herein.
In another general embodiment, a method includes forming a bottom yoke above a substrate: forming one or more conductors above the bottom yoke and separated therefrom by an insulating material; and forming a top yoke above the one or more conductors and separated therefrom by an insulating material. At least one of forming the bottom yoke and forming the top yoke includes a procedure comprising: applying a first mask; depositing a first ferromagnetic layer in an area not masked by the first mask; depositing a nonmagnetic layer above the first ferromagnetic layer; applying a second mask above the nonmagnetic layer; and depositing a second ferromagnetic layer in an area not masked by the second mask.
Referring to
A first ferromagnetic top yoke 108 and bottom yoke 110 wrap around the one or more conductors in a first of the arms 102. On either side of the conductor 106 are via regions 113 and 115, where the ferromagnetic top yoke 108 and ferromagnetic bottom yoke 110 are coupled through a low reluctance path.
A second pairing of a ferromagnetic top yoke 114 and bottom yoke 116 wraps around the one or more conductors in a second of the arms 104. Furthermore, ferromagnetic top yoke 114 and ferromagnetic bottom yoke 116 are coupled together through a low reluctance path at the via regions 117, 119.
The particular configuration of
The width of the first ferromagnetic layer in either or both of the yokes 108, 110 may be different than the width of the second ferromagnetic layer thereof in a direction parallel to a plane of deposition of the first ferromagnetic layer. This variation in width may occur in a direction parallel to the longitudinal axes of the conductors 106 and/or the direction perpendicular thereto.
With continued reference to
With continued reference to
In one approach, the first and second ferromagnetic layers are plated layers. In another approach, only one of the ferromagnetic layers is plated. In yet another approach, at least one of the ferromagnetic layers is formed by a dry process known in the art, such as sputtering, ion beam deposition (IBD), etc.
In the via regions having the low reluctance path between the top and bottom yokes, the magnetic layers may be in direct contact, or may be separated by a thin nonmagnetic layer, which may be any nonmagnetic material known in the art, such as ruthenium, copper, gold, alumina, silicon oxides, polymers, etc.
The particular configuration of
The particular configuration of
In one approach, the laminate structure of at east one of the yokes further comprises a second nonmagnetic layer above the second ferromagnetic layer, and a third ferromagnetic layer above the second nonmagnetic layer. Where the nonmagnetic layers are insulators, this configuration effectively breaks the electrical conduction path, thus reducing the current losses within the yokes. This design strategy may be used to further decrease losses in the yokes by further increasing the number of layers that are created in either or each of the yokes.
Several methods for constructing structures of the various embodiments of the present invention are possible. In one approach, a wet etch is used on film yokes masked by photoresist. However, this process was deemed to cause the laminated layers to become very thick thus making it difficult to wet etch and produce a reliable structure.
Another process for forming laminated yokes is electroplating in which a seed layer would be formed, followed by a layer of patterned photo resist, followed by plating the bottom layer of the yoke. Subsequently, a nonmagnetic layer would be formed, which has to be conducting to plate on. Where the nonmagnetic layer is insulating, formation of an overlying laminate is inhibited, and additional processing steps and cost would have to be incurred. Finally another magnetic layer is plated above the nonmagnetic layer. However, this process favors the laminates that are both nonmagnetic and electrically insulating, which ultimately makes this process ineffective.
According to a preferred embodiment, each ferromagnetic layer of the yoke structure is plated using a separate resist mask and using a separate dry deposition of insulation material to form the lamination layers of the yoke. Consequently, each yoke is electroplated in two separate steps. In this manner any insulation material such as, but not limited to SiOx, AlOx, SiN, etc. can be selected, and the insulation layer need not be etched, and electroplating of the yoke layers can be retained. One result of this process is that the lateral extent of the first ferromagnetic layer of the yoke formed by electroplating may be greater than subsequent ferromagnetic layers of the yoke formed by electroplating. More specifically, an inductor with laminated top and/or bottom yokes with the respective yoke being formed by multiple resist steps corresponding to the number of ferromagnetic layers in the top and/or bottom yoke.
For each layer of laminated ferromagnetic material, it is preferred that a separate photolithography mask step, a separate seed layer and a separate plating step are implemented, with insulating laminate layers that are dry deposited and that are not etched during the patterning process to form the yokes. The separate lithography steps therefore result in the lateral extents of the outside edges of each successive laminated ferromagnetic layer being smaller in extent than the previous laminated ferromagnetic layer outside edges. In this manner, there is alignment tolerance in successive lithography steps.
This process allows one to extend to “n” layers from a manufacturing perspective, where “n” greater than two is possible due o the additional photo steps and electroplating steps. Because of these independent masking and plating steps, the edges of the top layer and the edges of the bottom layer are independently defined, thus allowing one to purposefully control the amount of overlap between the layers, which would not be possible using wet etching.
In another approach, the first ferromagnetic layer of a top and/or bottom yoke of a thin film inductor has a greater width than the second ferromagnetic layer thereof in at least one direction, preferably where the second ferromagnetic layer is positioned above the first ferromagnetic layer. In one approach, the edges of the second ferromagnetic layer between which the width is measured are each indented by about 0.5 to about 20 microns from edges of the first ferromagnetic layer aligned generally parallel thereto.
In another approach, the edges of the second ferromagnetic layer of a thin film inductor, between which the width is measured (whichever edges those happen to be), have physical characteristics of being mask-defined. Such characteristics may include vertical sidewalls, a step-like corner or corners, lack of nonuniformities that one would expect from other processes such as milling or etching, etc.
In yet another embodiment, the edges of the second ferromagnetic layer of one or more of the yokes of a thin film inductor, between which the width thereof is measured and edges of the first ferromagnetic layer that are aligned generally parallel o the edges of the second ferromagnetic layer are physically characterized as being independently defined.
A method 500 of making a thin film inductor according to one embodiment is depicted in
In step 502, a bottom yoke is formed above a substrate. Any suitable process may be used, such as plating, sputtering, masking and milling, etc. The top and bottom layers of the bottom yoke in this and other embodiments may be constructed of any soft magnetic material, such as iron alloys, nickel alloys, cobalt alloys, ferrites, etc. The nonmagnetic layer between the top and bottom layers may be any nonmagnetic material known in the art, such as ruthenium, copper, gold, alumina, silicon oxides, polymers, etc.
In step 504 of
In step 506, a top yoke is formed above the one or more conductors and separated therefrom by an insulating material, which may be the same as or different than the insulating material between the conductor(s) and the bottom yoke. The top yoke may have the same, a similar, or different compositional structure as the bottom yoke.
One skilled in the art, upon being apprised of the present specification, will appreciate how to adapt known processes to perform the various steps listed herein.
Forming the bottom yoke, as in step 502, and/or forming the top yoke, as in step 506, may include one or more of steps of the illustrative process depicted in FIG. 6.A-6D, which include cross sectional views of an illustrative laminated yoke configuration.
In one approach, a width of the first ferromagnetic layer is different than a width of the second ferromagnetic layer in a direction parallel to a plane of deposition of the first ferromagnetic layer.
In another embodiment, the first and second ferromagnetic layers are plated, so the nonmagnetic layer is formed by deposited using a dry process such as by sputtering, etc.
Advantages provided using the methodology of
Furthermore, in yet another approach, an electronic device may be formed in, on and/or above the substrate and coupled to an inductor in accordance with any embodiment,
In any approach, the dimensions of the various parts may depend on the particular application for which the thin film inductor will be used. One skilled in the art armed with the teachings herein would be able to select suitable dimensions without needing to perform undue experimentation.
In use, the thin film inductors may be used in any application in which an inductor is useful.
In one general embodiment, depicted in
Additional applications, according to various embodiments include power conversion for LED lighting, power conversion for solar power, etc. For example, one illustrative approach may include a solar panel, a power converter having an inductor as described herein, and a battery.
In one illustrative embodiment, depicted in
In yet other approaches, the thin film inductor may be integrated into electronics devices where they are used in circuits for applications other than power conversion. The inductor may be a separate component, or formed on the same substrate as the electronic device.
In yet another approach, the thin film inductor may be formed on a first chip that is coupled to a second chip having the electronic device. For example, the first chip may act as an interposer between the power supply or converter and the second chip.
Illustrative systems include mobile telephones, computers, personal digital assistants (PDAs), portable electronic devices, etc. The power supply or converter may include a power supply line, a transformer, etc.
While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of an embodiment of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
This application is a divisional of U.S. patent application Ser. No. 13/347,571, filed Jan. 10, 2012, and which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13347571 | Jan 2012 | US |
| Child | 14207319 | US |
